A low-pressure system to the north of Western Australia has rapidly intensified into a category two cyclone, with a blue alert issued for a stretch of the Pilbara coast.

Tropical Cyclone Veronica was sitting about 500 kilometres north-west of Broome and 545 kilometres north of Port Hedland on Wednesday afternoon, and could reach the coast by the weekend, threatening communities from Port Hedland to Exmouth.

Veronica is expected to track slowly west-southwest over the next 24 to 48 hours, before turning more southward later in the week.

The Bureau of Meteorology is warning as it takes that path, it is set to intensify into a severe tropical cyclone, bringing destructive winds.

"Basically, there is really warm sea surface temperatures, wind shear is quite low over the system, and there's a lot of moisture in the atmosphere as well because there's a fairly strong surge of monsoonal north-westerlies to the north of the system," BOM duty forecaster Pete Clegg said.

The BOM earlier said the cyclone could eventually become a category five system.

Veronica strongest cyclone of season

Mr Clegg said there remained a significant level of uncertainty as to what path the cyclone might take, and so it was not yet clear where and when it might affect the WA coast.

"It's got very weak steering winds affecting it at the moment, so that's why it's moving quite slowly," he said.

"The general direction over the next 24 to 48 hours, we're fairly confident with that west-southwest direction, but after that point there's a couple of different features in the atmosphere that could help to steer it to the south.

"But by that stage it could be such a strong system that the direction that it steers may be influenced by the strength of the system itself, and that's why we're pretty concerned about it reaching the Pilbara coast."

With Western Australia relatively unaffected by cyclones this season Mr Clegg said Veronica would likely have the strongest impact on the west coast for 2018/19.

"We have had a few in the region but they've generally been offshore, so this will be the most significant impact that we will have seen for the season for WA so far," he said.

Residents in affected communities are being urged to monitor the latest forecasts and advice.

Blue alert from Mardie to Pardoo

The Department of Fire and Emergency Services (DFES) said the cyclone blue alert covered people in communities between Mardie and Pardoo, including Port Hedland, South Hedland, Wickham, Roebourne, Point Samson, Karratha and Dampier.

"Although there is no immediate danger you need to start preparing for dangerous weather and keep up to date," DFES said.

DFES said gales with gusts to 100 kilometres per hour were expected to develop between Pardoo and Mardie from as early as Friday evening, likely extending further west along the Pilbara coast over the weekend.

Destructive winds with gusts to 130 kilometres per hour are forecast to develop along the coast during the weekend, with a period of very destructive winds with gusts in excess of 165 kilometres per hour possible as the cyclone intensifies and approaches the coast.

Widespread very heavy rainfall conducive to major flooding is likely along parts of the coast over the weekend.

People along the coast are also being warned of the potential for a very dangerous storm tide as the cyclone approaches over the weekend.

Tides are likely to rise significantly above the normal high tide mark with damaging waves and very dangerous coastal inundations.

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It was an aptly named Sunday today, with temperatures reaching 28 degrees in the city, and hitting 30 degrees for western Sydney.
A very weak seabreeze and increasing cloud will keep the temperatures up overnight, with the eastern suburbs looking to only drop to 16-to-18 degrees overnight.
On Monday, it will be another warm one.